Method of Forming an Agent and its Use in Desulphurisation

ABSTRACT

The present disclosure is directed to a desulphurisation agent for removing sulphurous species from a diluent or process stream, and a use of such agent. In some examples, the agent may include a compound of manganese, pore forming particles and a compound of copper. The agent may be introduced into or mixed with the diluent or process stream to effectuate removal of sulphorous species from the diluent or process stream.

CROSS-REFERENCE TO RELATED APPLICATIONS

This divisional application claims priority to U.S. patent applicationSer. No. 12/443,885, filed Oct. 8, 2009, which is a 35 U.S.C. §371patent application claiming priority to PCT/GB2007/003744, filed on Oct.2, 2007, which claims priority to U.K. patent application 0619396.5,filed Oct. 2, 2006, the disclosures of which are incorporated herein byreference in their entirety.

BACKGROUND

This invention relates to porous articles and specifically porousarticles with controlled macro porosity which are usable to removeunwanted or required species from process streams or diluents.

It is known that process streams or diluents may contain either unwantedor required species which have to be removed from the process stream ordiluent. For example, natural gas can contain compounds of mercuryand/or arsenic and it is often necessary to cause desulphurisation ofgas and/or liquid streams.

WO 98/17374 (the entire disclosure of which is herein incorporated byreference) discloses a desulphurisation agent which comprises at leastone compound of manganese and at least one compound of iron. The agentmay be in the form of shaped particles which may be porous with a porevolume of from 0.1 to 0.6 ml/g. Sorption materials such as coppercompounds and/or zinc compounds may be provided on the surface or withinthe pores of the agent or within the bulk phase.

It is an object of this invention to provide a porous article which hascontrolled macro porosity and which can have adsorbents and/or catalyticspecies applied thereto or loaded therein for the processing of diluentsor process streams.

It has been found that by controlling the macro porosity in this contextthe effectiveness of such porous articles is enhanced.

SUMMARY

According to a first aspect of the invention, there is provided a methodof forming an agent for removing or separating a species from a diluentor process stream, e.g. a desulphurisation agent, the method comprisingmixing the following:

-   -   at least one compound of manganese;    -   preferably at least one compound of iron and/or copper and/or        zinc;    -   pore forming particles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a comparison of the intrusion volume ofExample 1 material (line A) and of the Example 2 material (line B);

FIG. 2 is a schematic representation of the apparatus used; and

FIG. 3 is a graph showing the performance of the various materials.

DETAILED DESCRIPTION

The agent may comprise at least one compound of manganese and ironand/or copper and/or zinc which are present in the weight or order range8:1 to 1:8, preferably in the range 3:1 to 1:3, although all otherinclusive ranges may be used. The inclusion of copper compounds orcopper is beneficial because it will scavenge lower concentrations ofsulphur compounds as well as arsine.

Compounds of copper may be present in the range of 5:1 to 1:5 (Cu:Mn)and zinc compounds may be present in the range of 5:1 to 1:5 (Zn:Mn).

The agent, e.g. the desulphurisation agent, may be in the form of anextrudate or granulate depending on the desired use. The form of theagent will be determined by the amount of liquid mixed with thecomponents and the process of formation used.

Preferably, the pore forming particles are thermoplastic particles.

The use of thermoplastic spheres gives subsequently-fired ceramicextrudates pre-selected porosity and pore size. Because of thehydrophilic nature of the spheres these voids may be interconnected withthe window sizes up to 30% of the sphere diameters. Preferably thethermoplastic spheres make up between about 5% and about 95% of thetotal volume of the paste, preferably between 10% and 30%. Suitablespheres are sold under the trade name EXPANCEL.

Where the agent is an extrudate, different or additional agents can beincluded in the paste to give the fired extrudates added porosity andpore structure. These additional or different pore forming agents can becategorised into three groups:

-   -   Macroscopic structural pore formers.    -   Microscopic pore structure modifiers, and    -   Additional pore formers.

By macroscopic structural pore formers we mean additives which willprovide channelled structure within the fired extrudates.

The strut size of this channel structure will be in the millimetre rangebetween 0.5 and 10, or more preferably between 1 to 6 mm. Thesemacroscopic structural pore formers can be selected from sphericalmaterials such as expanded polystyrene beads, fibres of aspect ratiobetween 1 to 5 made from polymers or natural materials, andthree-dimensional specially designed shapes such as reticulatedpolyurethane foam pieces and injection moulded thermoplastic spatialpatterns.

By microscopic pore structure modifiers we mean the additives willprovide morphological modification of the existing pores formed by otheragents, say, thermoplastic spheres. The major function of themodification is to increase the specific surface area of the extrudatesat the microscopic level by adding extra fine pores into the system. Thepore size formed for this purpose is in the sub-micron range between 1and 1000 nm, and more preferably between 50 and 800 nm. Thesemicroscopic structural pore modifiers can be selected from sphericalmaterials such as latex suspensions, chemicals evolving gas at elevatedtemperatures such as aluminium hydroxide, calcium carbonate andmagnesium carbonate. The additional pore formers may be natural organicmaterials such as ground almond shell, olive stone, coconut-shell, andthe like. The materials are relatively cheaper than thermoplasticspheres and give off less environmentally hazardous emissions duringfiring.

Preferably, the at least one compound of manganese is selected from theoxide, hydroxide and/or carbonate (e.g. hydroxycarbonate).

The at least one compound of iron, copper or zinc may be selected fromthe oxide, hydroxide and/or carbonate (e.g. hydroxycarbonate).

The compounds may be used as the only components or there may beincluded a promoter such as a compound of an element selected fromGroups 1A, 18, VA and VIII of the Periodic Table, for example one ormore of potassium hydroxide nickel hydroxide and sodium hydroxide. Theconcentration of the promoter is preferably in the range of from 0 toabout 10%.

Binders may also be present, for example cement, aluminium, days,silicates, organic binders and so on.

In particular the binders may be any substance suitable for the purposeof giving a high green strength of the granulates or extrudates once theliquid medium is removed. Examples of organic binders include polyvinylalcohol, polyvinyl acetate, polyethylene glycol, polysaccharides,cellulose derivatives, agar, starches, flours and gelatins; otherinorganic binders include kaolin, colloidal silica and colloidal aluminaand fine aluminium hydroxides.

In another embodiment the binder may be a polymerisable monomer which onaddition of the appropriate catalyst and initiator, polymerises to setthe structure of the shaped product. A hydrophilic binder is preferableand one which can be reversibly dehydrated such that an active speciescan be dispersed in the monomer which after polymerisation anddehydration holds the active species in a dispersed form and may preventreaction with for example oxygen, carbon dioxide etc by polymer coatingand which on rehydration renders the active species available forreaction.

The polymerisable monomer may also be added to a preformed porous bodywith the sole function of holding dispersions of active species in thepolymer coating on the surface and within the pores of the perform. Ondehydration, at a temperature below which the dehydration is areversible process, the polymer maintains the dispersion of activespecies in a controlled environment. On rehydration the active speciesbecome available for reaction/absorption. Alternatively the polymer isheated above the temperature for reversible hydration to a temperatureat which the polymer is partially or fully carbonised so exposing theactive species.

The thermoplastic particles are preferably spheres which may be solid,hollow or foamed with micro-porosity, the hollow thermoplastic spheresbeing most preferred. In the case of foamed thermoplastic spheres, theexpansion ratio (size after expansion divided by size before expansion)should be in the range between 10 to 40, preferably between 20 and 30.To reduce the risk of chemical contamination of the products thecomposition of the thermoplastic spheres should be preferably free fromalkali metals, phosphorous, calcium, magnesium, chlorine, sulphur,silicon, and other metal ions. From the environmental point of view thechemical composition of the thermoplastic-spheres should preferably befree from ammonia, chlorine, sulphur and other nitrogen containingamino-groups.

Both the performing particles, e.g. thermoplastic spheres, (and otheragents) may be solution treated to coat an active chemical or chemicalsonto their surface to locally modify the chemical or mineralogicalcomposition of the fired porous extrudates. An active catalyst materialor its precursor, e.g., salt, may be uniformly coated onto the fillersurface and subsequently transferred onto the inner surface of thepores. A significant cost saving and a much more uniform catalystdeposition comparing with the traditional techniques, are thus obtained.Other active materials such as crystalline seeds, grain growthmodifiers, chemicals, and fine ceramic particles of the same ordifferent compositions of the matrix ceramic powder, may be incorporatedinto the solution either separately or in various combinations. Thesesolution treatments will result in a fully or partially crystallisedthin surface around the pores, example being amorphous silicate; a fineror coarser grain sizes within the surface layer of the pores, examplesbeing abrasive ceramic foams and special dielectric components; and athin surface coating of various chemical compositions and mineralphases, examples of which are highly corrosion resistant foams.

In a preferred feature the agent, e.g. desulphurisation agent, comprisesshaped particles. The particles may be presented in a variety of shapesand sizes preferably as spheres; extrudates, granules, tablets or thelike. The shaped material may require exposure to elevated temperaturesto achieve the optimum bond strength.

The use of thermoplastic spheres is particularly advantageous in thepreparation of catalysts and absorbents in that small extrudates,granules, rings, cylinders can be formed in a facile manner usinggranulation or low pressure extrusion techniques and on calcination ofthe shaped product the thermoplastic spheres decompose to formmacropores within the overall porosity. The higher the addition ofthermoplastic spheres to the original mix the higher the level ofmacroporosity. This has significant benefits in the utilisation ofactive catalyst/absorbent species on the inner pore surfaces of theshaped body.

The technique can be applied to catalysts and absorbents in which thebulk phase is based on metal oxides, hydroxides, carbonates etcparticularly for use in purification processes such as desulphurisationof hydrocarbons, halide removal from gases and liquids, the removal ofmercury and arsenic compounds from natural gas etc.

The macroporosity can be utilised for infiltration, partially or fully,by metallic species in the form of alloys such as silver. A silverinfiltrated porous body may be used for the removal of mercury fromgaseous streams by forming an amalgam with the silver. In anotherembodiment the shaped body is subject to temperatures at which thethermoplastic spheres undergo reversible dehydration. This has potentialin reactions such as hydrolysis of COS or oxygen scavengers where thegas/liquid to be purified is water saturated and the purificationprocess requires the presence of liquid water for the process toproceed.

The species may be used in a fixed bed, a fluid bed or a moving bed. Thechoice of the reactor system will depend on generated requirements andthe nature of the gas stream, e.g. sour feed. Particle sizes of about 3to about 6 mm are particularly useful in a fixed bed. In a fluid bed,the particle size is preferably in the range about 20 to about 120 μm,most preferably about 30 to about 100 μm.

For the moving bed, the particle size is preferably in the range about120 to 600 μm, most preferably about 200 to about 500 μm.

The method of the invention may be enhanced by the incorporation ofmaterials with sorption properties. Such materials may be addedaccording to the physical form of the desulphurisation agent. They maybe added on to the surface or within the pores of a porousdesulphurisation agent or in the bulk phase. Such materials may becatalytically active. The materials (which may be included either singlyor in combination) are preferably oxides, carbonates, silicates,phosphates of alkali metals, alkaline earths, rare earths, Zn, Co, NiMo, Cr, Cu, Ti Zr, Si Al, precious metals. The materials may beincorporated within the material of the invention by impregnation,deposition, coforming, precipitation techniques well known to thoseskilled in the art of catalyst preparation. The content of the sorptionmaterials may range from about 0 to 40% by weight, preferably in therange 2 to 20% by weight.

In a preferred feature of the invention, other reagents are associatedwith the desulphurisation agent to react with other substances presentin the stream to be treated at from about ambient to about 250° C. Onesuch reagent is an alkaline reagent such as alkali metal hydroxide orsilicate, the alkali metal is preferably sodium. Such an alkalinereagent will react with halides or strongly acidic gases present in thesour feed such as SOx to form halide or sulphide respectively (which maybe recovered later). The reagents may be impregnated into thedesulphurisation agent or incorporated into the bulk phase by othermeans well known to those skilled in the art of catalyst preparation.

The spent desulphurisation agent of the invention may be regenerated byexposure to an oxidising atmosphere e.g. air at elevated temperature.The presence of steam when regenerating may be beneficial.

In another aspect the method of the present invention includes thefurther step of exposing the spent agent to oxidation at elevatedtemperature to remove the sulphur compounds and regenerate the agent forre-use.

The sulphur compound to be removed may be hydrogen sulphide gas or a lowmolecular weight mercaptan such as propyl mercaptan. The hydrocarbonstream may be liquid or gas or both, examples being natural gas, towngas, industrial waste gas, coke oven gas, coal gas, liquid or gas frompetroleum plant oil refinery. Effluent streams from biomass digesters,general industrial process may also be treated.

The method may be performed at pressures ranging from about atmosphericto about 100 atmospheres without adverse effect.

The desired species may be mixed according to the teachings of earlierprior art to form compositions for the use in removal of species from adiluent or process stream.

The effectiveness of these species is thought to be enhanced by the useof pore-forming particles which provide high levels of controlledmacroporosity.

In order that the invention may be more fully understood reference ismade to the accompanying examples.

EXAMPLE 1

The following composition was mixed

MnO₂ 4 (parts by weight) ZnCO₃ 3 CuCO₃ 2 Thermoplastic Spheres 0.1Binder 0.6 Water 2.6

The resulting mixture was extruded at a low pressure (<0.4 MPa). Theresulting extrudate was shaped and fired to provide particles of anagent having a diameter of 3 mm, a pore volume of 0.4-0.5 ml/g and asurface area >45 m²/g. The material was effective in low temperaturedesulphurisation of gaseous and liquid hydrocarbon additives.

EXAMPLE 2

The following composition was mixed

MnO₂ 2 (parts by weight) ZuCO₃ 3 CuCO₃ 4 Thermoplastic Spheres 0.1Binder 0.6 Water 2.6

The resulting mixture was extruded, shaped and fired to provideparticles of an agent having a diameter of 3 mm, a pore volume of0.45-0.5 ml/g and a surface area of >45 m²/g.

The material was used in low temperature desulpherisation of gaseous andliquid hydrocarbon feed stocks.

FIG. 1 provides a comparison of the intrusion volume of Example 1material (line A) and of the Example 2 material (line B).

To show the effectiveness of the two species a series of experimentswere conducted to determine the species' ability to remove sulphur froma propane process stream.

FIG. 2 provides a schematic representation of the apparatus used,wherein the material 1 is packed into two tanks 10, 11, the outlet 10 hof the first tank 10 being connected by conduit 20 to the inlet 11 a ofthe second tank 11.

Gas to be treated is directed into the inlet 10 a of the first tank 10,through the material 1 and then via the outlet 10 b and conduit 20 tothe inlet 21 a of the second tank 11 where it travels through thematerial 1 before exiting the tank 21 via outlet 11 b, whereupon it isanalysed by gas chromatography.

FIG. 3 provides a graph showing the performance of the various materialsfor a 10 minute contact time with the propane diluent, where the dataindicated by C-1, C-2 and C-3 relates to the material of Example 1, thedata indicated by D-1, D-2 and D-3 relates to the material of Example 2.

Clearly, a number of different materials may be used together, or inisolation.

The results show that significant amounts of the sulphur-containingspecies were removed.

The effectiveness of these species is thought to be enhanced by the useof pore-forming particles which provide high levels of controlledmacroporosity.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

1-26. (canceled)
 27. A desulphurisation agent for removing sulphurousspecies from a diluent or process stream, the agent comprising at leastone compound of manganese, pore forming particles and at least onecompound of copper.
 28. Use of an agent for desulphurisation of aprocess or diluent stream, the agent comprising at least one compound ofmanganese, at least one compound of copper, and pore forming particles.29. The agent of claim 27, further comprising at least one of a compoundof iron and a compound of zinc.
 30. The agent of claim 29, wherein aratio of the compound of manganese to the at least one compound of ironand/or copper and/or zinc is between 8:1 and 1:8 by weight.
 31. Theagent of claim 29, wherein a ratio of the compound of manganese to theat least one compound of iron and/or copper and/or zinc is between 3:1and 1:3 by weight.
 32. The agent of claim 27, wherein the pore formingparticles comprise thermoplastic particles.
 33. The agent of claim 27,wherein the pore forming particles comprise thermoplastic spheres. 34.The agent of claim 33, wherein between 5% and 95% of a total volume ofthe agent comprises thermoplastic spheres.
 35. The agent of claim 33,wherein between 10% and 30% of a total volume of the agent comprisesthermoplastic spheres.
 36. The agent of claim 27, wherein the compoundof manganese comprises at least one of an oxide, a hydroxide and acarbonate.
 37. The agent of claim 29, wherein each of the at least onecompound of iron, copper, and zinc is selected from an oxide, ahydroxide and a carbonate.
 38. The use of the agent of claim 28, whereinthe agent is introduced into the process or diluent stream.
 39. The useof the agent of claim 28, wherein the agent is mixed with the process ordiluent stream.
 40. The use of the agent of claim 28, wherein heat isapplied to the agent.